The fluctuation hypothesis of hydrogen bonding

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Abstract
This paper opens a series of articles devoted to the theoretical calculation and physical interpretation of the band shapes in the infra-red and Raman spectra of H-bonded liquids on the basis of the fluctuation model of hydrogen bonding. In the present introductory article general features of the fluctuation model are discussed and the fluctuations of H-bond configurations are classified as dynamical and statistical ones. It is shown that in liquids such as water or alcohols the statistical fluctuations play a dominant role, i.e. the band broadening originates from disorder in equilibrium positions and orientations of the molecules in liquid. This idea does not yet permit us, however, to make the direct calculations of the spectral band shape on the basis of structural data. A semi-empirical approach is proposed instead which allows us to calculate in the frames of the fluctuation model the band shapes in the infra-red and Raman spectra of numerous water complexes with organic bases and of pure H2O and D2O starting from spectra of HOD in similar complexes. The comparison of calculated and experimental spectra will be used in the following papers to justify the physical model.

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